1. Field of the Invention
The present invention relates to an ink tank for use in an ink jet recording apparatus for performing the recording by discharging the ink from a recording head onto a recording medium.
2. Related Background Art
The recording apparatuses such as a printer, a copying machine and a facsimile can perform the recording of an image composed of dot patterns based on image information onto a recording medium such as a paper or a plastic thin plate.
The above-described recording apparatuses can be classified into an ink jet system, a wire dot system, a thermal system, and a laser beam system, depending on the recording system. Among them, a recording apparatus of the ink jet system can perform the recording by discharging or flying ink (recording liquid) droplets from the discharge orifices of a recording head to attach them onto a recording medium.
In recent years, numerous recording apparatuses have appeared, and been required to realize the faster recording, higher resolution, higher image quality, and lower noise. One of the recording apparatuses which can meet such demands is the ink jet recording apparatus as above mentioned. The ink jet recording apparatus allows for the non-contact printing, because the ink is discharged from the recording head onto the recording medium in printing, and thus can produce very stable recording images.
The ink jet recording apparatus has increasing demands due to its many merits. In particular, one can make the most of such merits for the color printing.
The ink jet recording apparatus having the ability of color printing, in the main current, performs the printing by using four color inks consisting of three colors of C (cyan), M (magenta) and Y (yellow), in addition to Bk (black). Hence, an ink tank is required to store inks of three or four colors as above cited.
FIG. 1 is an appearance view schematically illustrating a conventional ink tank.
The conventional ink tank 600 as shown in FIG. 1 has an atmosphere communicating opening 609 for communicating the air between the inner and outer portions of the ink tank 600, and is mounted on a recording head 601.
The ink tank may be of a separate type in which each color ink is separately stored, or an integral type in which the ink tanks for storing three or four color inks are integrated. Also, the system of ink tank for storing the ink therein may be made by providing a sponge for producing a negative pressure internally, or providing partly a sponge except where the ink is stored as such.
FIG. 2 is a cross-sectional view schematically showing one constitutional example of a conventional ink tank for storing two color inks. This ink tank has the advantage that the ink tank can be disposed in a smaller arrangement space over the ink tank of separate type wherein a separate ink tank is prepared for each color ink, and is mostly used as one example of constitution in the color recording apparatuses.
This conventional example, as shown in FIG. 2, comprises a vessel composed of an outermost vessel 501 and an outer lid 512, this vessel being partitioned by an inner wall 515 into two sections, each comprising an atmosphere communicating opening 509, 508 for communicating the air between the outside and inside of the vessel, a porous member 507, 506 having the ink absorbed up to an ink level as indicated, and an ink supply opening 511, 510 for supplying the ink absorbed in the porous member 507, 506 to the outside. Note that the outermost vessel 501 and the outer lid 502 are thick members, while the inner wall 515 is a thin member.
The outermost vessel 501 and the outer lid 502 are welded together at a welding part 503, the inner wall 515 and the outer lid 502 at a welding part 512, and the outermost vessel 501 and the inner wall 515 at a welding part 513.
This ink tank, which takes such a constitution and is applicable to the recording apparatuses capable of the color printing, has multiple ink tanks simply integrated, with an atmosphere communicating opening for each color disposed on an outer lateral face of each ink tank, whereby there is a higher possibility of ink leakage proportional to the number of ink tanks (for ink colors).
Also, the multi-color tank has a greater length of welding part in making the ink tank than the monochrome tank, resulting in higher possibility of ink leakage due to welding failure or exfoliation. In addition, the welding part 512 between the wall of adjacent tanks (inner wall 515 in FIG. 2) and the outer lid 502, for example, is required to be welded reliably to cause no color mixture of inks, and may be often regulated on manufacture with respect to the process management or welding method.
Furthermore, the ink tank of a type in which the multi-color ink tanks are integrated has a problem that the amount of ink for each color to be stored is relatively small as compared with the ink tank for use on the monochrome recording apparatus. Thus, it is conceived that the amount of ink to be stored may be increased by making thinner the wall between color ink tanks to reduce the wasteful space, but the outer wall susceptible to external forces is usually obliged to be thicker from the aspect of mechanical strength. Thus, the thickness of inner wall is made thinner, but the thickness of outer wall and that of inner wall are greatly different, resulting in unstable welding conditions with a higher probability of welding failure. On the other hand, if the outer wall is made thinner to attain equivalent welding conditions, its mechanical strength becomes weak, with a risk that the ink may be forced out due to an increase in internal pressure of the ink tank, causing ink leakage through the atmosphere communicating opening, for example, when a force is applied to the outer wall.
Also, because the wall between color ink tanks is made thin as above described, its mechanical strength is weak, and when there is a welding part in the region easily touchable from the outside, there is a risk that the welding part is easily peeled off, if an external force is applied to that welding part, and if it is peeled off, there is a risk that a serious problem of ink leakage or color mixture in the ink tank may arise.